Electrically conductive fabrics have, in general, been known for some time. Such fabrics have been manufactured by mixing or blending a conductive powder with a polymer melt prior to extrusion of the fibers from which the fabric is made. Such powders may include, for instance, carbon black, silver particles or even silver- or gold-coated particles. When conductive fabrics are made in this fashion, however, the amount of powder or filler required may be relatively high in order to achieve any reasonable conductivity and this high level of filler may adversely affect the properties of the resultant fibers. It is theorized that the high level of filler is necessitated because the filler particles must actually touch one another in order to obtain the desired conductivity characteristics for the resultant fabrics.
Such products have, as mentioned briefly above, some significant disadvantages. For instance, the mixing of a relatively high concentration of particles into the polymer melt prior to extrusion of the fibers may result in undesired alteration of the physical properties of the fibers and the resultant textile materials.
Antistatic fabrics may also be made by incorporating conductive carbon fibers, or carbon-filled nylon or polyester fibers in woven or knit fabrics. Alternatively, conductive fabrics may be made by blending stainless steel fibers into spun yarns used to make such fabrics. While effective for some applications, these "black stripe" fabrics and stainless steel containing fabrics are expensive and of only limited use. Also known are metal-coated fabrics such as nickel-coated, copper-coated and noble metal-coated fabrics, however the process to make such fabrics is quite complicated and involves expensive catalysts such as palladium or platinum, making such fabrics impractical for many applications.
It is known that polypyrrole may be a convenient material for achieving electrical conductivity for a variety of uses. An excellent summary in this regard is provided in an article by G. Bryan Street of IBM Research Laboratories Volume 1, "Handbook of Conductive Polymers", pages 266-291. As mentioned in that article, polypyrrole can be produced by either an electrochemical process where pyrrole is oxidized on an anode to a desired polymer film configuration or, alternatively, pyrrole may be oxidized chemically to polypyrrole by ferric chloride or other oxidizing agents. While conductive films may be obtained by means of these methods, the films themselves are insoluble in either organic or inorganic solvents and, therefore, they cannot be reformed or processed into desirable shapes after they have been prepared.
Accordingly, it has been suggested that the polypyrrole may be made more soluble in organic solvents by providing one or two aliphatic side chains on a pyrrole molecule. More recently, it has been suggested that the pyrrole may be polymerized by a chemical oxidation within a film or fiber (see U.S. Pat. No. 4,604,427 to A. Roberts, et al.). A somewhat similar method has been suggested wherein ferric chloride is incorporated into, for instance, a polyvinyl alcohol film and the composite is then exposed to pyrrole vapors resulting in a conductive polymeric composite.
Another method for making polypyrrole products is described in U.S. Pat. No. 4,521,450 to Bjorklund, et al. wherein it is suggested that the oxidizing catalyst be applied to a fiber composite and thereafter exposed to the pyrrole monomer in solution or vapor form. A closely related process for producing electrically conductive composites by precipitating conductive pyrrole polymer in the interstitial pores of a porous substance is disclosed in U.S. Pat. No. 4,617,228 to Newman, et al.
However, while the examples of the aforementioned patents to Roberts, et al., Bjorklund, et al. and Newman, et al. show increased conductivity for various non-porous synthetic organic polymer films, impregnable cellulosic fabrics, and porous substances, respectively, these processes each have various drawbacks. For example, they require relatively high concentrations of the pyrrole compound applied to the host substrate. Another problem inherent to these processes is the requirement for separate applications of pyrrole monomer and oxidant, with one or the other first being taken up by the fabric, film, fiber, etc. and then the other reactant being applied to the previously impregnated host material. This dual step approach may involve additional handling, require drying between steps, involve additional time for first impregnation and then reaction. The process of Bjorklund, et al. as pointed out by Roberts, et al. has the additional deficiency of not being applicable to non-porous polymeric materials. On the other hand, the Roberts, et al. process requires use of organic solvents in which the pyrrole or substituted pyrrole analog is soluble, thus requiring handling and recovery of the organic solvent with the corresponding environmental hazards associated with organic solvents. Still further, it is, in practice, difficult to control the amount of conductive polymer deposited in or on the substrate material and may result in non-uniform coatings, loosely adherent polypyrrole ("pyrrole black") and inefficient use or waste of the pyrrole monomer. Furthermore, as will be shown hereinafter, under the conditions used to effect epitaxial deposition of the in status nascendi forming polymer of pyrrole or aniline, the presence of organic solvents interferes with the deposition and prevents formation of an electrically conductive film on the textile material.
On the other hand the electrochemical deposition of polypyrrole on the surface of textiles could only be achieved if these fabrics would be per se electrically conductive. H. Naarmann, et al. describes such a process in DE No. 3,531,019A using electrically conductive carbon fibers or fabrics as the anode for the electrochemical formation of polypyrrole. It is obvious that such a process would be inoperative on regular textiles which are predominantly insulators or not sufficiently conductive to provide the necessary electrical potential to initiate polymerization.
Another conductive polymer which can be obtained by an oxidative polymerization from an aqueous solution and which has similar properties to polypyrrole is polyaniline. Such products are described in a paper by Wu-Song Huang, et al. In the Am Chem. Soc. Faraday Trans. 1, 1986 82, 2385-2400. As will be shown later herein, polyaniline can be epitaxially deposited in the in status nascendi form to the surface of textile materials resulting in conductive textile materials much like the corresponding materials made from pyrrole and its derivatives.